Do you have any solid idea how it happened? I'm wondering about Reward Assignment via random website and entering seed?

yes - I tried to claim Bitcoin Private and Bitcoin Diamond. Most likely the the BCD Electrum wallet was a scam. There are lots of reports like this on bitcointalk.org. I knew there was a risk. But I never expected that it would hit me that hard.

@dworf Thanks for sharing your experience. I'm really sorry to hear that this has happened to you; the robbing scum bags will get sorted out by karma! Not much consolation I know, but I appreciate you sharing your misfortune so that others may benefit.